Abstract

Aims: To compare the outcome of shock wave lithotripsy (SWL) on post-percutaneous nephrolithotomy (PCNL) residual fragments (RFs) versus primary stones of the same size through a matched pair study. Methods: Patients with a single 5-15 mm fragment 3 months after PCNL were enrolled (study group n = 59). The control group (n = 67) consisted of all adult patients with a single 5-15 mm renal stone. Results: The success rate of SWL was significantly higher in the study group (81.4 vs. 59.7%; p = 0.008; OR: 2.95). With a cutoff point of Hounsfield units (HU) 750: the success rate was significantly lower in patients with a stone HU ≥ 750 (OR: 3.488). This HU cutoff value had no effect on the outcome of SWL in patients with post-PCNL RF (p = 0.14). On the other hand, the outcome of SWL was significantly more favorable in control group when HU < 750 (p = 0.02). Conclusion: The success rate of SWL was 2.95-fold higher for post-PCNL RFs than in a stone burden-matched control group. The likelihood of stone clearance after SWL was 3.488-fold greater when HU was less than 750. This effect of HU was more prominent in patients receiving SWL for their primary stones while SWL was evenly effective on post PCNL RFs with different HUs.

Comments
1

How to manage patients with residual fragments/stones after less successful stone removal is an important and sometimes difficult decision. In the present article the authors have compared the effects of SWL on residuals, after PNL, with SWL used as primary procedure for stone burdens of similar size.

The finding that SWL was more effective in patients who had residuals after PNL than in patients who were primarily treated with SWL is surprising.

Two possible explanations for this outcome are presented:
a. Previous PNL with pneumatic lithotripsy might have rendered the stones more fragile. This conclusion is supported by the recorded lower density of stones after PNL.
b. Another factor that might have contributed to the result is that the PNL procedure has dilated the collecting system and thus facilitated fragment elimination resulting in a higher SFR. This latter mechanism gives support to the previously suggested value of artificial hydronephrosis during SWL [1].

Clinical relevance: SWL might be an alternative that more commonly should be considered for patients with residual stones/fragments after stone removal with endourological procedures. Moreover, induced hydronephrosis might be beneficial for disintegration or fragment elimination or both, as suggested in a recent report.

How to manage patients with residual fragments/stones after less successful stone removal is an important and sometimes difficult decision. In the present article the authors have compared the effects of SWL on residuals, after PNL, with SWL used as primary procedure for stone burdens of similar size.
The finding that SWL was more effective in patients who had residuals after PNL than in patients who were primarily treated with SWL is surprising.
Two possible explanations for this outcome are presented:
a. Previous PNL with pneumatic lithotripsy might have rendered the stones more fragile. This conclusion is supported by the recorded lower density of stones after PNL.
b. Another factor that might have contributed to the result is that the PNL procedure has dilated the collecting system and thus facilitated fragment elimination resulting in a higher SFR. This latter mechanism gives support to the previously suggested value of artificial hydronephrosis during SWL [1].
Clinical relevance: SWL might be an alternative that more commonly should be considered for patients with residual stones/fragments after stone removal with endourological procedures. Moreover, induced hydronephrosis might be beneficial for disintegration or fragment elimination or both, as suggested in a recent report.
Reference
1. AbdelRazek M, Hassan A, AbdelKader MS, Abolyosr A. SWL outcome in artificial hydronephrotic vs. non-hydronephrotic kidney for preschool children with high-density renal stones.
World J Urol. 2018 Aug 30 [Epub ahead of print]